Add git hash as version information via Bazel stamp. (#46)

ansible-puller used to include its git sha as version
https://github.com/teslamotors/ansible_puller/blob/e93c507dae6f92fc4ed2ec205a86cf6603ed7467/build-release.sh.
This logic was missed out during the migration to Bazel. This PR adds it
back to be consistent so that the Prometheus metric can show the current
git build hash.

.bazelrc

@@ -0,0 +1,7 @@
+# Bazel stamp variable generations
+build --workspace_status_command=$(pwd)/ws_status.sh
+
+# For release
+# To use it: bazel COMMAND --config=release
+build:release --compilation_mode=opt
+build:release --stamp

BUILD

@@ -58,6 +58,7 @@ go_library(
         "@com_github_spf13_pflag//:pflag",
         "@com_github_spf13_viper//:viper",
     ],
+    x_defs = {"main.Version": "{STABLE_GIT_COMMIT}"}
 )
 
 #

README.md

@@ -140,12 +140,12 @@ or, without bazel
 
 #### Building a Production Release
 
-`bazelisk build --platforms=@io_bazel_rules_go//go/toolchain:linux_amd64 //...`
+`bazelisk build --config=release --platforms=@io_bazel_rules_go//go/toolchain:linux_amd64 //...`
 
 #### Building Production Packages
 
-* `bazelisk build //:ansible_puller_deb`
-* `bazelisk build //:ansible_puller_rpm`
+* `bazelisk build --config=release //:ansible_puller_deb`
+* `bazelisk build --config=release //:ansible_puller_rpm`
 
 
 #### Debugging an Ansible Run

ws_status.sh

@@ -0,0 +1,4 @@
+#!/usr/bin/env bash
+# Generates the data used by the stamping feature in bazel.
+
+echo STABLE_GIT_COMMIT "$(git rev-parse HEAD)"